1. Field of the Invention
The present invention relates to a magnetic sensor for detecting the speed of rotation for example of a gear-shaped magnetic rotor.
2. Description of the Related Art
FIG. 49 is a front view of a conventional magnetic sensor unit. FIG. 50 is a side view of the conventional magnetic sensor taken along line L--L of FIG. 49 wherein a gear-shaped magnetic rotor detected by the magnetic sensor is also shown in the figure. FIG. 51 is a cross-sectional view of a main sensor unit. FIG. 52 is a cross-sectional view of a case. FIG. 53 is a front view of the main sensor unit. FIG. 54 is a front view of the case. In FIGS. 49-53, the magnetic sensor includes: a main sensor unit 1 made up of an electric insulating resin on which an electric component is mounted; and a case 2 made up of an electric insulating resin covering the main sensor unit 1 in a sealed fashion. The main sensor unit 1 includes a main part 1a, a seating 1b, an intermediate part 1c, and a connector 1d. The main part 1a includes a Hall element 3 which is the most important component of the magnetic sensor, a permanent magnet 4, and a circuit board 7 on which a circuit pattern 6 is formed and on which electronic components 5 are mounted.
The intermediate part 1c has a substantially rectangular shape with a small length wherein the seating 1b with the shape of a circular step is formed on one end of the intermediate part 1c such that the axis of the seating 1b is coincident with that of the intermediate part 1c. The end face of the intermediate part 1c is formed into a substantially rectangular shape, and the diameter of the seating 1b is less than the side length of the intermediate part 1c.
The exterior circumferential surface of the seating 1b serves as a fitting-in portion 1e fitted into the case 2 which will be described in detail late. An O-ring groove 1f is formed along the circumference of the fitting-in portion 1e, and an O-ring 9 is disposed in the O-ring groove 1f. When the components are assembled into a complete magnetic sensor, the seating 1b is fitted in an opening at an end of the case 2 so that a closed space is created in the case 2. The main part 1a is disposed on the principal surface of the seating 1b in such a manner that the main part 1a extends in a direction perpendicular to the principal surface of the seating 1b.
The main part 1a is formed into the shape of a substantially rectangular and long plate, and one end of the main part 1a is connected at a right angle to the principal surface of the seating 1b. The circuit board 7 is mounted on one principal surface of the main part 1a. The permanent magnet 4 is mounted at a right angle on the other end of the main part 1a. The Hall element 3 serving as the sensor element for detecting the magnetic material approaching the sensor element is disposed on the outer-side principal surface of the permanent magnet 4.
The connector 1d extends from one side face of the intermediate part 1c. After extending from the end face of the intermediate part 1c in a direction perpendicular to the main part 1a, the connector 1d bends into a direction parallel to the axis of the main part 1a. That is, the connector 1d extends from the end face of the intermediate part 1c into the form of an L-like shape and thus the connector 1d has an offset in position from the central axis of the main sensor unit 1. Terminals electrically connected to the circuit pattern 6 of the main part 1a are embedded in the connector 1d. A connecting cavity is formed in the L-shaped end portion of the connector 1d and the terminals 8 project into the connecting cavity so that a connector of an external device can be fitted into the connecting cavity.
Of four side faces of the intermediate part 1c, the three side faces other than the side face having the connector 1d serve as a holder receptor 1g held by the holder of the case 2.
The main sensor unit 1 is produced by forming the main part 1a, the seating 1b, the intermediate part 1c, and the connector 1d in an integral form including the terminals 8 embedded therein by means of molding. After that, the Hall element 3, the permanent magnet 4, and the circuit board 7 are attached.
The case 2 is produced in an integral fashion by means of molding in such a manner as to include: a sleeve 2a in the form of a cylinder with a closed end; a flange which is formed at an open end of the sleeve 2a by increasing the wall thickness of the end portion of sleeve 2a in outward radial directions; a supporting projection 2c extending outward in a radial direction from the flange 2b; and a holder including three plates 2d extending from the principal surface of the flange 2b in a direction parallel to the sleeve 2a.
The sleeve 2a produced into the form of the cylinder with the closed end has a length similar to that of the main part 1a of the main sensor unit 1, and has a diameter slightly greater than the width of the main part 1a. The main part 1a of the main sensor unit 1 is placed in the sleeve 2a in such a manner that the central axis of the main part 1a is coincident with that of the sleeve. The Hall element 3 disposed on the end of the main part 1a is in contact with the closed end of the sleeve 2a. The sleeve 2a has a receiving portion 2e, inside the sleeve at its open end, for receiving the seating 1b of the main sensor unit 1.
As described earlier, the O-ring 9 is disposed on the seating 1b of the main sensor unit 1. The inner diameter of the receiving portion 2e formed at the open end of the sleeve 2a is slightly greater than the diameter of the seating 1b. The seating 1b is fitted into the sleeve 2a in such a manner that the open end of the sleeve 2a is closed with the seating 1b . The receiving portion 2e is in tight contact with the O-ring 9 and thus serves as sealing means by which a tightly sealed space is created in the case 2. The main part 1a of the main sensor unit 1 is placed in this tightly sealed space.
The flange 2b is formed by increasing the wall thickness of the open end portion of the sleeve 2a outward in radial directions over the entire circumference. The supporting projection 2c extends outward in a radial direction from the flange 2b. A fixing hole 2f is formed in the end portion of the supporting projection 2c in such a manner that the fixing hole 2f extends in parallel to the axis of the sleeve 2a. The magnetic sensor is fixed to a desired location with a screw (not shown) fitted into the fixing hole 2f formed in the supporting projection 2c.
The holder is composed of three plates 2d extending from the principal surface of the flange 2b in the direction parallel to the axis of the sleeve 2a. These three plates 2d are formed so that the principal surface of each plate is in contact with corresponding one of the three side faces, serving as the holder receptor 1g, of the intermediate part 1c of the main sensor unit 1. That is, the three plates 2d are located on the intermediate part 1c in such a manner that the principal surface of each plate 2d is in contact with the holder receptor 1g, while the connector 1d projects through the opening of the holder 2c. Since each principal surface of the holder 2c is in contact with the holder receptor 1g of the intermediate part 1c, the main sensor unit 1 is prevented from rotating relative to the case 2.
The upper end portions 2g of the plates 2d are bent inward into an L shape in cross section along the entire length, by means of high-temperature caulking. The upper end portions 2g of the holder 2c are in contact with the end face of the intermediate part 1c of the main sensor unit 1 so that the upper end portions 2g serve as a separation stopper for preventing the main part 1a from moving outward from the inside of the sleeve 2a.
The magnetic sensor constructed in the above-described manner is fixed to a desired location with a screw fitted through the fixing hole 2f formed in the supporting projection 2c. When a gear-shaped magnetic rotor 20 made up of a magnetic material disposed near the magnetic sensor is rotated, the recessed portions 20a and the protruding portions 20b alternately approach and pass by the Hall element 3. As a result, a variation occurs in the magnetic field which emerges from the permanent magnet 4 and is applied to the Hall element 3. The variation in the magnetic field is detected as a variation in voltage by the Hall element 3. The variation in voltage generated by the Hall element 3 is then converted by the electronic components 5 into a pulse signal. The electric signal in the pulse form is transmitted to an external device (not shown) via the terminals 8 of the connector 1d so as to detect the speed of rotation of the magnetic rotor 20.
In the production process of the magnetic sensor, a resin part of the main sensor unit 1 is first produced by forming the main part 1a, the seating 1b, the intermediate part 1c, and the connector 1d in an integral form including the terminals 8 embedded therein by means of molding. The Hall element 3, the permanent magnet 4, and the circuit board 7 are then mounted on the above resin part. The case 2 is also produced in an integral fashion by means of molding. Then the main sensor unit 1 is inserted into the case 2, and the upper end portions 2g of the plates 2d of the case 2 are caulked at a high temperature so that the main sensor unit 1 and the case 2 are combined together into a completely integral form. The caulking is performed as follows. First, the main sensor unit 1 is inserted into the case 2. Then the assembly is held with a hand at the sleeve 2a or the supporting projection 2c, and a hot tip is put on and pressed against the upper end portions of the holder 2c so that they are bent by means of pressure and heat. In the above caulking process, since the connector 1d is located at an offset location relative to the central axis of the magnetic sensor, it is easy to put the hot tip on the target positions in the rear of the intermediate part 1c.
In the conventional magnetic sensor described above, the main sensor unit 1 and the case 2 each have a wide variety of types which are different in details wherein each type of main sensor unit has one type of case which should be combined with that main sensor unit. An operator should select a main sensor unit and a case which match each other, and combines them into a single form.
Although there are a great number of different types of main sensor units 1 and cases 2, those parts which can be the same in structure, the same structures are employed for convenience of production. In the specific example of the conventional magnetic sensor described above, of various components, the intermediate part 1c and the holder 2c are each constructed into the same structures and are employed in various types of magnetic sensors. However, this creates a chance that a magnetic sensor is produced with a wrong combination of parts.
To avoid the above problem of the wrong combination, a manual or table is prepared so that operators can combine correct parts by referring to the manual or table. However, wrong combination can still occur, and the probability of the wrong combination increases with the number of types of parts. This causes a reduction in production yield.
Thus, it is a general object of the present invention to solve the above problems. More specifically, it is an object of the present invention to provide a magnetic sensor which can be easily produced with a correct combination of parts without requiring an operator to pay particular attention.